Iodine (for example in the form of Lugol's solution or tincture of iodine) has long been recognized as an effective biocide. U.S. Pharmacopoeia and other similar publications in many countries have documented this property of iodine since 1830. Iodophores have been noted for their similar properties since 1960.
These iodines have been recognized for their bioactivity in man, animals, and in types of bacteria in plants and their seeds. In fact, a deficiency of iodine has been shown to prevent the attainment of maximum health, growth, and reproductive success.
It has been recently shown that the active component in all biocidal iodines is thermodynamically free iodine, which is uncomplexed or pure elemental iodine (I.sub.2), as described in the Schmidt and Winicov article "Detergent/Iodine Systems" in Soap and Chemical Specialties, August 1967. It has also been recently shown that thermodynamically free iodine when fed to a mammal has a much decreased effect upon the thyroid compared to iodide, or iodine/iodide mixtures or mixtures of polyhalides (see Thrall and Bull in their article "Differences in the Distribution of Iodine and Iodide in the Sprague--Dawley Rat" in Fundamental and Applied Toxicology, 15, 75-81 (1990)).
The term thermodynamically free iodine describes iodine that is free from complexing. Thermodynamically free iodine in aqueous solution may dissociate into many hydrolyzed forms, depending upon concentration and/or pH, for example HIO (or also known as HOI), some of which are biocidal in nature. If a solution of aqueous iodine (I.sub.2 +hydrolyzed biocidal forms where appropriate) could be reliably generated at any concentration of thermodynamically free iodine less than supersaturation, and remain stable at that level, it would allow the manufacture of many devices useful in water treatment, instrument sterilization, use as a source of nutritional iodine, plus other medicinal uses including the treatment of IDDs (Iodine Deficiency Disorders), chemical uses, and catalytic uses. For example, if a device could reliably produce a desired concentration of thermodynamically free iodine into a pH buffered fluid such that the thermodynamically free iodine remained unhydrolyzed and of known concentration despite moderate changes in ambient temperature, it would allow the treatment of many non-thyroidal IDDs and other medical conditions known to respond to treatment with iodine, such as in U.S. Pat. No. 4,816,255 of Ghent, with a much reduced toxicity (toxicity meaning thyroid complication found with other forms of iodine, iodides, iodine/iodide mixtures or polyhalides).
In an effort to produce biocidal iodine compounds, many methods, both chemical and mechanical in nature, have been devised. To date, however, these methods have had limited use and commercial success for reasons attributable to iodine's chemical and physical properties such as low solubility in H.sub.2 O, reactivity, easy contamination or the production of poly-halides and iodides and other potentially noxious adjuvants which inhibit the presence of thermodynamically free iodine, or its use in some applications.
Thermodynamically free iodine in all biocidal iodine solutions, whether alcohol/water, surfactant/water or other complexing agent/water, is confined to the water phase. Further, thermodynamically free iodine is usually found in solution in concentrations less than that of the total titratable iodine of the solution. For example, Lugol's solution, where potassium iodide (KI) is used to create a reservoir of iodine as I.sub.3.sup.- through the relationship I.sub.2 +nI.sup.- I-+I.sub.n, the solubility of elemental iodine is, increased to, for example, 1% (w/v); however, the amount of thermodynamically free iodine detectable is only circa 0.018% (w/v) or 180 ppm.
The germicidal capacity of these iodine formulations is dependent upon the continued release of thermodynamically free iodine from the reservoir of titratable iodine, as the thermodynamically free iodine in solution is depleted through dilution, contamination or biocidal activity. It has therefore been the goal of researchers to develop a practical means of creating this reservoir from which pure thermodynamically free iodine may be released alone, with no other adjuvants, into water in a controlled fashion.
Attempts have been made to develop a means to mechanically contain an amount of metallic elemental iodine in contact with water, as shown in U.S. Pat. No. 3,408,295 issued Oct. 29, 1968 in the name of John A. Vaichulis and in U.S. Pat. No. 4,384,960 issued May 24, 1983 in the name of Richard D. Polley. These methods, however, have not been totally effective in restraining micro-particles (and sometimes macro-particles) of iodine crystals from being carried away by the water flow. Further, these methods cannot prevent the contamination of the iodine reservoir by undesirable substances which may reduce the effectiveness of the reservoir, or facilitate the release of unwanted contaminants into the product stream containing the wanted thermodynamically free iodine and still further cannot provide stable levels of thermodynamically free iodine below the saturation level for iodine in a fluid in contact with the iodine.
Attempts have also been made to develop a chemical means of providing a reliable supply of thermodynamically free iodine. The chief fault of such systems (for example Lugol's solution, tincture of iodine, iodophores) is that a loss of solvent (i.e. water lost through evaporation) increases the total percentage of iodine in a volume and therefore, given iodine's relative insolubility, increases the toxic effect of the remaining solution (through recrystallization of elemental iodine) and subsequently reduces the availability of thermodynamically free iodine.
Another problem is that by chemical means, the level of thermodynamically free iodine in water is usually restricted to about 60% of the maximum solubility of thermodynamically free iodine in water (which is circa 0.03%). This is about 180 ppm (0.018%), and is usually found to be much less than that. For example, an iodophore of 3.75% titratable iodine may achieve maximum strength of less than 40 ppm of thermodynamically free iodine after dilution while having 75 ppm of titratable iodine. This discrepancy between the level of thermodynamically free iodine and the amount of titratable iodine makes the field testing for iodine concentration very cumbersome.
Where chemical adjuvants are used to increase the reservoir of titratable iodine, the adjuvants may act as an unwanted toxicant. There are many applications for the use of iodine in the medical field (i.e. the irrigation of wounds or incisions during surgery) and one adjuvant mixture used for this purpose was P.V.P.I. (poly(N-vinyl-2-pyrrolidone)-iodine). Eventually it was realized that the P.V.P. (poly(N-vinyl-2-pyrrolidone)) macro molecule tended to lodge in the lymph glands of a patient, causing problems with the function of the gland. This is one example of adjuvants causing undesirable side effects.
Finally, the thermodynamically free iodine should be as pure as practically and economically obtainable, for the end uses to which it is to be put. Any existing chemical means of releasing thermodynamically free iodine will likely release undesirable contaminants into the final product.
It is an object of the present invention to provide a reliable method of obtaining pure thermodynamically free iodine.
It is a further object of the invention to provide a device for obtaining pure thermodynamically free iodine.
It is a further object of this invention to show a method of, and a device for, obtaining thermodynamically free iodine in any predetermined concentration.